1. Field of the Invention
The present invention relates to a node device and a network resource reservation method for transfer of data packets such as IP (Internet Protocol) datagrams using ATM (Asynchronous Transfer Mode) networks.
2. Description of the Background Art
In a case of carrying out the communication using the Internet, data transmitted by a sender is converted into a data packet called IP datagram which is defined at an IP (Internet Protocol) level, and the converted data packet is delivered to a receiver.
The conventional data packet delivery service defined by the IP is a Best-Effort system, that is, a delivery system which does not provide any guarantee regarding the data packet delivery (so that the data packet may be lost but no measure against a packet loss is provided) but which makes the best effort to attempt the data packet delivery. In other words, conventionally, no quality has been guaranteed for the delivery of the data packet at the IP level.
In this regard, in recent years, there is a discussion in the IETF (Internet Engineering Task Force) regarding the quality to be provided for the delivery of the data packet at the IP level. For example, there are propositions of new services which specify various qualities for the data packet delivery, such as Guaranteed Quality of Service, Predictive Quality of Service, and Controlled Delay Quality of Service.
These new services can be briefly described as follows.
(1) Guaranteed Quality of Service
This is a service which guarantees that the data packet delivery is carried out within a prescribed period of time for sure. For the quality of service, the transmission rate value is to be requested.
(2) Predictive Quality of Service
This is a service which guarantees that the data packet delivery is carried out within a prescribed period of time at high probability (that is, this is a service which guarantees to deliver most data packets to their destinations within a prescribed period of time). For the service quality, the service level (1, 2, 3) is to be requested, where the relative delay is less for the smaller service level value. In addition, an upper limit for a required transfer time with respect to each service level is set up at each communication node.
(3) Controlled Delay Quality of Service
This is a service in which the service level is to be requested as the quality of service but an upper limit for a required transfer time is not set up. In this service, the data packet delivery delay changes dynamically, but the data packet delivery can be made in a shorter time than the conventional Best-Effort service.
(4) Best-Effort Service
This is a service which does not guarantee any quality, so that no quality of service is to be requested.
On the other hand, there is also a proposition of a resource reservation protocol called RSVP (Resource ReSerVation Protocol) which becomes necessary in order to provide the above described services.
This RSVP is characterized in that the resource reservation is carried out according to a request from a destination user terminal. The destination user terminal transmits a reservation message called Resv message to a source user terminal so as to attempt the reservation of the receiving quality of service which is described within the Resv message. Then, when the Resv message is received by a data packet communication node (router device) which relays the data packet sent from the source user terminal to the destination user terminal, whether it is possible to accept the resource reservation required in providing the receiving quality of service indicated by this Resv message or not is judged, and if it is judged possible, the reservation request is accepted and this Resv message is transmitted to the source user terminal.
In a case of carrying out the data packet transfer at the IP level using virtual connections established on ATM networks, in which data are switched and transferred in units of fixed length data packets called cells, there has been no need for the guarantee of the quality of service for the data packet transfer at the IP level and the reservation of the network resource conventionally, so that the quality at the IP level has not been taken into consideration at a time of the data packet delivery. Conventionally, only a scheme for accommodating data packets to virtual connections has been discussed, and a scheme for establishing virtual connections in consideration to the above described provision to provide a requested quality of service at the packet level has not been discussed.
In addition, in a case of carrying out the data packet transfer using ATM networks, when a message requesting a change of the quality of service (such as an Resv message transmitted from a destination user terminal to a source user terminal in the RSVP, for example) is received, there is a need to change attributes (a service category, an amount of resources to be reserved, etc.) of virtual connections which accommodate data packets corresponding to that message, and in conjunction with this change of attributes, there are cases in which it is necessary to newly establish virtual connections in order to be able to provide the newly requested quality of service. In such cases, the data packet transfer cannot be carried out until the virtual connections are newly established, so that the undesirable increase of the packet transfer delay can be caused.